Long Term Evolution (“LTE”) of the Third Generation Partnership Project (“3GPP”), also referred to as 3GPP LTE, refers to research and development involving 3GPP Release 8 and beyond, which is the name generally used to describe an ongoing effort across the industry aimed at identifying technologies and capabilities that can improve systems such as the universal mobile telecommunication system (“UMTS”). The goals of this broadly based project include improving communication efficiency, lowering costs, improving services, making use of new spectrum opportunities, and achieving better integration with other open standards. Further developments in these areas are also referred to as Long Term Evolution-Advanced (“LTE-A”).
The evolved UMTS terrestrial radio access network (“E-UTRAN”) in 3GPP includes base stations providing user plane (including packet data convergence protocol/radio link control/medium access control/physical (“PDCP/RLC/MAC/PHY”) sublayers) and control plane (including radio resource control (“RRC”) sublayer) protocol terminations towards wireless communication devices such as cellular telephones. A wireless communication device or terminal is generally known as user equipment (“UE”) or a mobile station (“MS”). A base station is an entity of a communication network often referred to as a Node B or an NB. Particularly in the E-UTRAN, an “evolved” base station is referred to as an eNodeB or an eNB. For details about the overall architecture of the E-UTRAN, see 3GPP Technical Specification (“TS”) 36.300, v8.5.0 (2008-05), which is incorporated herein by reference. The terms base station, NB, eNB, and cell refer generally to equipment providing the wireless-network interface in a cellular telephone system, and will be used interchangeably herein, and include cellular telephone systems other than those designed under 3GPP standards.
Orthogonal frequency division multiplex(ing) (“OFDM”) is a multi-carrier data transmission technique that is advantageously used in radio frequency based communication systems such as 3GPP E-UTRAN/LTE/3.9G, IEEE 802.16d/e Worldwide Interoperability for Microwave Access (“WiMAX”), IEEE 802.11a/WiFi, fixed wireless access (“FWA”), high performance radio local area network (“HiperLAN”), digital audio broadcast, (“DAB”), digital video broadcast (“DVB”), and others including wired digital subscriber lines (“DSLs”). The OFDM systems typically divide available frequency spectrum into a plurality of carriers that are transmitted in a sequence of time slots. Each of the plurality of carriers has a narrow bandwidth and is modulated with a low-rate data stream. The carriers are closely spaced and orthogonal separation of the carriers controls inter-carrier interference (“ICI”).
When generating an OFDM signal, each carrier is assigned a data stream that is converted to samples from a constellation of admissible sample values based on a modulation scheme such as quadrature amplitude modulation (“QAM,”) including binary phase shift keying (“BPSK”), quadrature phase shift keying (“QPSK”), and higher-order variants (16QAM, 64QAM, etc), and the like. Once phases and amplitudes are determined for the particular samples, the samples are converted to time-domain signals for transmission. A sequence of samples, such as a 128-sample sequence, is collectively assembled into a “symbol.” Typically, OFDM systems use an inverse discrete Fourier transform (“iDFT”) such as an inverse fast Fourier transform (“iFFT”) to perform conversion of the symbols to a sequence of time-domain sample amplitudes that are employed to form a time domain transmitted waveform. The iFFT is an efficient process to map data onto orthogonal subcarriers. The time domain waveform is then up-converted to the radio frequency (“RF”) of the appropriate carrier and transmitted. A particular issue for system operation including OFDM is calibration of frequency of a local oscillator in the user equipment and absolute time at the user equipment so that an OFDM signal can be accurately detected and demodulated.
As wireless communication systems such as cellular telephone, satellite, and microwave communication systems become widely deployed and continue to attract a growing number of users, there is a pressing need to accommodate a large and variable number of communication devices transmitting a growing range of communication applications with fixed communication resources. The 3GPP is currently studying various potential enhancements to the 3GPP LTE Release 8 to specify a new system called LTE-Advanced, which is supposed to fulfill the International Mobile Telecommunications-Advanced (“IMT-Advanced ”) requirements set by the International Telecommunications Union-Radiocommunication Sector (“ITU-R”). Topics within the ongoing study item include bandwidth extensions beyond 20 megahertz (“MHz”), communication link relays, cooperative multiple input/multiple output (“MIMO”), uplink multiple access schemes and MIMO enhancements.
To provide accurate detection of a received signal in a wireless communication system, it is generally necessary to transmit a reference signal that is embedded in a signal such as an OFDM signal to enable calibration of a local oscillator/clock, assistance with channel estimation, demodulation and decoding in a receiver. The reference signal can be constructed from a Gold code, and the reference signal is generally re-initiated in each subframe of a transmission sequence and depends on the user equipment identification (“UE ID”), the base station identification (“ID”), the physical resource block allocation, and the subframe number. Communication issues such as orthogonality between user equipment, suppression of mutual interference between user equipment, and the necessary accounting processes associated with the generation of a reference signal dependent on many variables results in substantial complexities and trade-offs for management of communication among a large number of end users.
In view of the growing deployment of communication systems such as cellular communication systems, further improvements are necessary for generation of reference signals. Therefore, what is needed in the art is a system and method that avoid the associated reference signal deficiencies of conventional communication systems.